1. Field of the Invention
The present invention relates to cargo container handling gantry cranes and, more particularly, it relates to an improvement in the wire rope reeving for the main cargo container handling trolley of such cranes. Specifically, it relates to an integrated wire rope reeving system for gantry cranes in which the same ropes perform both load hoist and trolley traversing operations.
2. Description of the Prior Art
Cargo container handling gantry cranes are arranged in the operating configuration to extend over a longitudinal expanse to transfer cargo containers horizontally from one deposition area to another. The heaviest of such gantry cranes are usually located in railroad yards and dockside in shipping ports around the world. Dockside cranes generally have either a horizontal sliding boom or a cantilever boom, the latter of which can usually be raised by rotating it around its inboard end. An example of this type of crane is disclosed in U.S. Pat. No. 5,765,981 developed by the assignee of the present invention. Long span yard cranes are typically supported by vertical structures located inboard from the ends of the crane gantry on rail- mounted wheels. The present invention can be utilized on any of these basic types of crane designs.
Reference is made to FIG. 1 of the drawings for a representation of the '981 type of crane having a cantilevered rotatable boom 11 for which the present invention can be utilized. The crane superstructure 13 is supported on crane truck wheels 15 which are mounted on dock rails which run parallel to the edge of the harbor dock. The superstructure supports a horizontal gantry 17 disposed generally mid-height thereon at an elevated location above the cargo container pickup and deposition areas 19. The gantry is supported from below by the main legs of the superstructure. In the cantilevered rotatable boom design, sheaves are disposed at the pinnacle 21 of the superstructure of the crane to guide wire rope reeving 23 which is used to rotate the outboard or cantilevered end of the boom to the upright raised stowed position. The outboard end or end and middle of the boom are also supported from the pinnacle by mechanical links 25 when the boom is lowered to level and the wire rope reeving 23 is slack. The load supporting links for the retractable gantry are collapsible. The wire rope reeving which raises the boom takes the load off the links which collapse when the cantilevered boom is rotated to its stowed position about its hinge point 27 at its inboard end proximate the superstructure.
While, in most typical dockside applications, the gantry of a cargo container handling crane is a slidable or raisable cantilever boom extending from a crane superstructure, other types of large gantry yard cranes supported at both ends are located in large cargo container storage or transfer areas. All of these cranes are similar to the '981 gantry type crane in that they employ a movable trolley 29, usually with a suspended operator's cab 31, which shuttles along the gantry 17 and boom 11 suspending a cargo container lifting spreader 33. The spreader can be raised or lowered from the crane gantry by the operator and engages the cargo containers 35 which are on the dock or shipboard to permit them to be lifted by the trolley for transport along the gantry to the deposition area 19 in a cargo container transport ship. The trolley is reciprocated along the gantry by a continuous wire rope system which is driven by wire rope drums located in the machinery house 37.
The cargo container lift trolley 29 mounted on rails on the crane gantry sections 11, 17, 41 can traverse from one end of the gantry to the other. The trolley suspends the cargo container lifting spreader 33 from fleet-through wire rope reeving by means of a detachable headblock which carries the wire rope suspension sheaves. Different length spreaders can be secured to the headblock to accommodate correspondingly different size containers.
There are essentially three types of wire rope reeving utilized in the prior art relating to the area of the present invention. They are each disclosed in the accompanying drawings which illustrate the apparatus and method by which the wire rope reeving for the main cargo transport trolley of a shoreside cargo container handling crane is employed. The wire rope reeving causes the traversing of the trolley on the gantry and hoisting and lowering of the cargo container lifting spreader.
Reference is made to FIGS. 2 and 3 for an illustration of the first type of basic wire rope reeving. For present purposes, it will be called a rope trolley container handling crane. There are two independent systems in this type of crane, and they are shown independently in the drawings for clarity. FIG. 2 shows the main trolley traversing drive of these gantry cranes. In the normal configuration of wire rope reeving, a pair of continuous traversing or drive wire ropes 43, driven by one or a pair of trolley drive drums 45, are secured to opposite ends of the cargo transport trolley 29. The term "continuous" generally means the wire rope is a continuous loop. Portions of the rope are either towing or slack depending on the direction of movement of the trolley, and the rope is always active and continuously in motion when the trolley moves.
For the rope trolley crane of FIG. 2, the drive drums 45 for the two pairs of main trolley drive ropes 43 are usually located somewhere mid-span on the gantry 17 in a machinery house 37 (FIG. 1). The pairs of drive ropes are oppositely wound and extend from the drums to reversing sheaves 47 disposed at opposite ends of the gantry through hydraulic rope tensioners 49. The pairs of ropes reverse direction and extend from the reversing sheaves to opposite ends of the cargo container transport trolley 29 movably located anywhere along the gantry. Operation of the drive drums moves the trolley in one direction along the gantry while reverse rotation of the drive drums reverses the tension and slack forces in the drive ropes and the movement of the trolley.
Reference is made to FIG. 3. In addition to the trolley drive ropes in a rope trolley crane, a separate system of hoist or lift ropes 51 for the lifting spreader 33 are integrated into the wire rope reeving system. They are very similar in orientation, operation, and location to the trolley drive ropes in the sense that they are also driven by drive drums 53 and run through reversing sheaves 47 at one end of the crane gantry 17. They differ, however, in that the two pairs of hoist ropes are not secured to the main trolley 29 but are reeved through fleet-through sheaves 55 mounted thereon whereby they travel downward to the lifting spreader and back up to the trolley and are dead-ended 57 at the opposite end of the gantry from the reversing sheaves. The hoist ropes operate independent of the trolley drive ropes and can be static or moving as the trolley moves along the gantry depending on whether the lifting spreader for the containers is being lifted or lowered while the trolley moves.
A second type of wire rope reeving for a crane will be called a machine trolley container crane, and it is shown in FIG. 4. The hoisting machinery 59 and the trolley traversing machinery 61 are both mounted on the trolley 29. The wire ropes 53 from the drums 63 of the hoist machinery mounted on the trolley go down to reversing sheaves on the lifting spreader headblock 33 and then go back up to the trolley and are dead-ended 65 to it. The ropes may be multiply-reeved between the headblock and the trolley sheaves to obtain a greater mechanical advantage. The trolley traversing machinery drives the trolley wheels 67 to move the trolley along the rails on the girder or boom of the gantry crane.
A third type of wire rope reeving will be called a semi-rope trolley container crane, and it is shown in FIG. 5. It is a combination of the first two types. The load hoist machinery is located in the machinery house on the gantry 17 and the wire ropes 53 are reeved the same as FIG. 3. The gantry traversing machinery 61 is mounted on the trolley 29 the same as the machine trolley type container crane of FIG. 4.
The three types of prior art cranes have the following disadvantages. With respect to the machine trolley-type crane, because the hoisting machinery and the trolley traversing machinery are mounted on the trolley, the trolley becomes extremely heavy and the crane girder structure and gantry required to support the trolley must necessarily be made stronger and heavier. In addition, as the machine trolley is driven by the wheels interconnected to the trolley traversing machinery, the wheels sometimes slip in foul conditions, such as the beginning of rainfall or when the rails have early morning frost.
For the lifted load anti-sway capability of the machine trolley-type crane, an electrical anti-sway control is available. However, the effect of sway control on a machine trolley crane is to jerk the heavy trolley back and forth to stop the load sway. This is uncomfortable for the crane operator, it is detrimental to the crane structure, and it requires large power inputs to effect the sway control.
For the rope trolley crane, the trolley carries only sheaves and it does not have either hoisting machinery or trolley traversing machinery mounted on it. Therefore, the trolley is light and the crane structure can be built correspondingly lightweight. Also, as the trolley is towed by the trolley ropes, there is no wheel slip. However, as the long length of the wire ropes for the hoist machinery and the trolley traversing machinery are reeved from the machinery house to both of the girder ends and to the trolley, the wire ropes experience considerable wear and require higher maintenance costs.
For the lifted load anti-sway capability of a rope trolley crane, a hydraulic-type sway dampening device is provided at the girder end sheaves or an electrical anti-sway control is available. The hydraulic-type sway dampening device is heavy and expensive, while the electrical anti-sway device has similar problems for the operator's comfort as with the machine trolley crane.
For the semi-rope trolley crane, the crane weight is between the other two types of cranes. The trolley traversing ropes are eliminated, but the trolley is driven by the wheels connected to the trolley traversing machinery, and the wheels are subject to slippage.
For the lifted load anti-sway capability of the semi-rope trolley crane, the conditions are nearly the same as that for the machine trolley crane.
The present invention provides an improvement in crane design which reduces the effects of these disadvantages in the prior types of crane.